Receivers are used in many applications to receive incoming radio frequency (RF) signals and convert them to baseband signals for desired processing. Various such receivers exist including cellular receivers, radio receivers, satellite receivers such as television satellite receivers, among many others.
A receiver is typically coupled to receive incoming RF signals from an antenna and process these signals in various stages, including amplification stages, filtering stages, down conversion stages, and the like. In many systems, received signals are of a very low power and accordingly must be amplified before further processing can occur. However, if signals are amplified too much, distortion may occur. Such distortion may include clipping in an analog-to-digital converter (ADC) of a receive path. If insufficient amplification is provided, signals of interest may be lost within the quantization noise of the ADC. Accordingly, many systems implement gain control in various manners. Some systems implement automatic gain control (AGC), which is often accomplished via an AGC algorithm.
A conventional AGC algorithm in a satellite receiver is typically based on a single power detector whose result will set the gain for the RF and baseband chains. This algorithm, however, is suboptimal for certain RF spectrum profiles. The most common AGC algorithm found in satellite receivers is based on a detector that is located at the output of a baseband ADC. The bandwidth of the filter in front of the ADC is usually tuned such that only the wanted channel is passed. As such, the detector is only exposed to the wanted channel power and is oblivious to the strength of adjacent channels.
While this scheme works well for satellite spectral profiles that have equal power channels, it is insufficient for degenerate cases where the wanted channel is different than the rest of the channels. For example, where the wanted channel is weaker than other received channels, the AGC algorithm will measure the power of the wanted channel and will set the gain as if all the channels are of equal power. But since in this case the rest of channels are stronger (e.g., “x” dB) than the wanted channel, the multi-tone power ratio (MTPR), which is the cumulative intermodulation distortion of all these other channels, will increase e.g., by “2X” dB, hence deteriorating performance of the desired channel considerably. A need thus exists for improved gain control.